Chartplotter goes dead when engine is cranked. - SailNet Community

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  • 5 Post By btrayfors
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Old 02-01-2012
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Chartplotter goes dead when engine is cranked.

I guess the DC load for the starter is so much that the voltage drops down below the minimum for the Raymarine A57D chartplotter and ST60 instruments turn off.

The 2 batteries installed, selected through the Perco 1/2/all switch, are new as of November and they are 2 interstate SRM-27B battery deep cycle batteries.

Anybody have an idea of how to somehow filter this load?

I was thinking about this theory since the batterys are bran new....
this sailboat came with a Westerbeke 2 cyl engine in 1983 and the previous owner removed it and installed a 3 cyl Beta Marine engine.

Maybe the existing cables cannot fully support the current draw to start this bigger engine. Althought the cable from both batterys are huge, I think they may be 1 AWG.
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Old 02-01-2012
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Sounds like there may be a couple things involved here, both of which may be related to the wiring.

The length of the engine starter cables between the engine and battery can be crucial, and more often than not they are much too light for the current draw of the starter. Heavier, shorter cables can make a huge difference in how much draw is placed upon the battery.

Instrument cables also tend to be very light, mainly because today's electronic devices have a very current draw. In my case, with my Lowrance HD7, I was experiencing the same problem. I changed the instrument cable from 20 gauge to 16 gauge and the problem was solved. The tip-off to me was the voltage reading on the HD7 was always below 12 volts unless the engine was running, but then it only rose to 12.5 at most. After changing the wiring the voltage reading on the HD7 was always above 12 volts with the engine shut down, and 14.2 when the engine was charging the batteries.

Hope this helps,

Gary
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The basic problem comes about by using the same battery or batteries for engine starting and for powering the chartplotter (and, by extension, other devices on board). Starters draw a lot of current and will pull the voltage down to levels which may be too low for certain devices, like your chartplotter.

While larger wires may help a bit, they won't solve the basic problem.

The real solution is to separate the house batteries from the start battery. With only two batteries onboard, that's difficult. Ideally, you'd use those two together as the house bank, and add a start battery dedicated to the engine. But, if that's not possible, then you will want to always start the engine with both batteries together, use larger wiring, and hope that will do the trick.

I'm NOT a fan of using house batteries for engine starting, for several reasons which have been hashed out over and over on this and other Boards. Some people do it and get away with it, but it's just not good practice. Much better to separate the start circuit from the house circuit.

IMHO,

Bill
RichH, tdw, mitiempo and 2 others like this.
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Old 02-01-2012
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Quote:
Originally Posted by travlineasy View Post
Sounds like there may be a couple things involved here, both of which may be related to the wiring.

The length of the engine starter cables between the engine and battery can be crucial, and more often than not they are much too light for the current draw of the starter. Heavier, shorter cables can make a huge difference in how much draw is placed upon the battery.

Instrument cables also tend to be very light, mainly because today's electronic devices have a very current draw. In my case, with my Lowrance HD7, I was experiencing the same problem. I changed the instrument cable from 20 gauge to 16 gauge and the problem was solved. The tip-off to me was the voltage reading on the HD7 was always below 12 volts unless the engine was running, but then it only rose to 12.5 at most. After changing the wiring the voltage reading on the HD7 was always above 12 volts with the engine shut down, and 14.2 when the engine was charging the batteries.

Hope this helps,

Gary
If you are wiring the boat to code, there should be no wires smaller than 16 gauge anyway. Even if smaller wires can handle the current, they are too fragile and easily chafed etc.

The best general purpose cable for adding electronics is two wire, red and yellow, white sheathed boat cable. In fact I keep 40 ft on board for repairs. The extra white sheath adds even more strength and chafe protection.
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I keep a roll of 16 on the boat as well, and for the same reasons. Many previously owned boats, however, have never been properly wired, which is a major part of most boat problems. You would be amazed at the number of poorly wired boats out there, many of which were wired by dealers.

Cheers,

Gary
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I once had a hard to trace voltage drop. Finally found the terminals contacts inside the either neither both switch had gummed up. A cleaning fixed it but installed separate starter battery circuit anyway. It could be your plotter wont be happy until it's isolated from the voltage drop of starting. My vhf ,gps sounder and plotter are all on completely separate source. It's a coast guard requirement for commercial vessels .Maybe a bit overkill for small boat but not expensive and good peace of mind when the galley light goes dim..
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